U.S. patent application number 09/989880 was filed with the patent office on 2003-05-22 for low temperature alkali metal electrolysis.
Invention is credited to Jacobson, Stephen Ernest, Mah, Dennie Turin.
Application Number | 20030094379 09/989880 |
Document ID | / |
Family ID | 25535557 |
Filed Date | 2003-05-22 |
United States Patent
Application |
20030094379 |
Kind Code |
A1 |
Jacobson, Stephen Ernest ;
et al. |
May 22, 2003 |
Low temperature alkali metal electrolysis
Abstract
A low temperature electrolysis process that can be used for
producing an alkali metal from an alkali metal halide is provided,
which comprises electrolyzing an electrolyte composition comprising
at least one alkali metal halide and a co-electrolyte comprising
(a) a halide or halides of Group IIIA, Group IB, or Group VIII
metals and (b) a halide-donating compound.
Inventors: |
Jacobson, Stephen Ernest;
(Princeton, NJ) ; Mah, Dennie Turin; (Wilmington,
DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
25535557 |
Appl. No.: |
09/989880 |
Filed: |
November 21, 2001 |
Current U.S.
Class: |
205/406 ;
75/711 |
Current CPC
Class: |
Y02P 10/138 20151101;
C25C 3/02 20130101; C25C 1/02 20130101; C22B 26/10 20130101; Y02P
10/134 20151101 |
Class at
Publication: |
205/406 ;
75/711 |
International
Class: |
C21B 015/00 |
Claims
What is claimed is:
1. A process for producing an alkali metal comprising electrolyzing
an electrolyte, which comprises or is produced by combining at
least one alkali metal halide and a co-electrolyte wherein said
co-electrolyte comprises (1) at least one halide selected from the
group consisting of Group IB halide, Group IIIA halide, Group VIII
halide, and combinations of two or more thereof and (2) a
halide-donating compound, which is capable of reacting with a Lewis
acid by donating a halogen atom.
2. A process according to claim 1 wherein said process is carried
out under a condition in which a molten layer of said alkali metal
is produced.
3. A process according to claim 2 wherein said process is carried
out at a temperature below about 200.degree. C., but is higher than
the melting point of said alkali metal.
4. A process according to claim 1 wherein said at least one halide
is selected from the group consisting of aluminum halide, boron
halide, antimony halide, iron halide, cobalt halide, nickel halide,
and combinations of two or more thereof.
5. A process according to claim 1 wherein said halide-donating
compound is RSO.sub.2X, RP(O)X.sub.2, or combinations thereof; R is
--CX'.sub.3, --N.dbd.PX.sub.3, --(CX.sub.2).sub.nCX.sub.3, or
combinations of two or more thereof; X is halogen; X' is hydrogen,
halogen, or combinations thereof; and n=3-7.
6. A process according to claim 1 wherein said halide-donating
compound is RSO.sub.2X, RP(O)X.sub.2, or combinations thereof; R is
--CX'.sub.3, --N.dbd.PX.sub.3, --(CX.sub.2).sub.nCX.sub.3, or
combinations of two or more thereof; X is halogen; X' is hydrogen,
halogen, or combinations thereof; and n=3-7.
7. A process according to claim 3 wherein said halide-donating
compound is RSO.sub.2X, RP(O)X.sub.2, or combinations thereof; R is
--CX'.sub.3, --N.dbd.PX.sub.3, --(CX.sub.2).sub.nCX.sub.3, or
combinations of two or more thereof; X is halogen; X' is hydrogen,
halogen, or combinations thereof; and n=3-7.
8. A process according to claim 4 wherein said halide-donating
compound is RSO.sub.2X, RP(O)X.sub.2, or combinations thereof; R is
--CX'.sub.3, --N.dbd.PX.sub.3, --(CX.sub.2).sub.nCX.sub.3, or
combinations of two or more thereof; X is halogen; X' is hydrogen,
halogen, or combinations thereof; and n=3-7.
9. A process according to claim 8 wherein said halide-donating
compound is selected from the group consisting of methanesulfonyl
chloride, trichlorophosphazosulfonyl chloride,
trichlorophosphazophosphoryl chloride,
trichlorophosphosphazosulfonyl chloride, and combinations of two or
more thereof.
10. A process according to claim 9 wherein said co-electrolyte
comprises aluminum chloride and methanesulfonyl chloride.
11. A process according to claim 9 wherein said co-electrolyte
comprises aluminum chloride and trichlorophosphazosulfonyl
chloride.
12. A process according to claim 9 wherein said co-electrolyte
comprises aluminum chloride and trichlorophosphazophosphoryl
chloride.
13. A process for producing an alkali metal comprising
electrolyzing an electrolyte, which comprises at least one alkali
metal halide and a co-electrolyte wherein said co-electrolyte
comprises (a) at least one halide selected from the group
consisting of Group IB halide, Group IIIA halide, and Group VIII
halide and (b) a halide-donating compound wherein said process is
carried out under a temperature below about 200.degree. C.; said
process is carried out such that a molten layer of said alkali
metal is produced; said at least one halide is selected from the
group consisting of aluminum halide, boron halide, antimony halide,
iron halide, cobalt halide, nickel halide, and combinations of two
or more thereof; and said halide-donating compound is RSO.sub.2X,
RP(O)X.sub.2, or combinations thereof; R is --CX'.sub.3,
--N.dbd.PX.sub.3, --(CX.sub.2).sub.nCX.sub.3, or combinations of
two or more thereof; X is halogen; X' is hydrogen, halogen, or
combinations thereof; and n=3-7.
14. A process according to claim 13 comprising raising said
temperature to higher than the melting point of said alkali metal
if said temperature is below the melting point of said alkali
metal.
15. A process according to claim 14 wherein X or X' is
chlorine.
16. A process according to claim 15 wherein said halide-donating
compound is selected from the group consisting of methanesulfonyl
chloride, trichlorophosphazosulfonyl chloride,
trichlorophosphazophosphoryl chloride,
trichlorophosphosphazosulfonyl chloride, and combinations of two or
more thereof.
17. A process according to claim 15 wherein said co-electrolyte
comprises aluminum chloride and methanesulfonyl chloride.
18. A process according to claim 15 wherein said co-electrolyte
comprises aluminum chloride and trichlorophosphazosulfonyl
chloride.
19. A process according to claim 15 wherein said co-electrolyte
comprises aluminum chloride and trichlorophosphazophosphoryl
chloride.
20. A process according to claim 17 wherein said alkali metal is
sodium and said alkali metal halide is sodium chloride.
21. A process according to claim 18 wherein said alkali metal is
sodium and said alkali metal halide is sodium chloride.
22. A process according to claim 19 wherein said alkali metal is
sodium and said alkali metal halide is sodium chloride.
23. A process for producing sodium comprising electrolyzing, in an
electrolytic cell, an electrolyte comprising (1) sodium chloride
and (2) a co-electrolyte selected from the group consisting of (a)
aluminum chloride and methanesulfonyl chloride, (b) aluminum
chloride and trichlorophosphazosulfonyl chloride, (c) aluminum
chloride and trichlorophosphazophosphoryl chloride, (d) aluminum
chloride and trichlorophosphosphazosulfonyl chloride, and (e)
combinations of any two of (a), (b), (c), and (d) wherein said
process is carried out under a temperature below about 200.degree.
C.
24. A process according to claim 23 wherein said process is carried
out under a condition such that a layer of molten sodium is
produced at the cathode and halogen is produced at the anode of
said cell.
25. A process according to claim 24 comprising raising said
temperature to higher than the melting point of said alkali metal
if said temperature is below the melting point of said alkali
metal.
26. A process according to claim 25 further comprising removing
said layer of molten sodium from said cell.
27. A process according to claim 26 further comprising separating
said sodium alkali metal thereby optionally producing a recovered
electrolyte.
28. A process according to claim 27 further comprising recycling
said recovered electrolyte.
29. A process according to claim 28 wherein said electrolyte
comprises said sodium chloride, said aluminum chloride, and said
methanesulfonyl chloride.
30. A process according to claim 28 wherein said electrolyte
comprises said sodium chloride, said aluminum chloride, and said
trichlorophosphazosulfonyl chloride.
31. A process according to claim 28 wherein said electrolyte
comprises said sodium chloride, aluminum chloride, and said
trichlorophosphazophosp- horyl chloride.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an electrolysis process and
electrolytes therefor for producing an alkali metal.
BACKGROUND OF THE INVENTION
[0002] Alkali metals are highly reactive elements and are not found
in elemental form in nature. Typical reducing agents, such as
hydrogen, are not strong enough to reduce the alkali metals from
their compounds to the metallic state. Electrolytic reduction is
necessary and was used historically in the classic experiments
leading to the discovery of the alkali metals in elemental form in
1807 by Sir Humphrey Davy. Electrolytic reduction is used for
industrial production of the alkali metals. The currently used
process, on a worldwide basis, is the so-called "Downs" Process,
which was introduced in the early part of the 20th century for the
production of sodium and lithium from their chlorides.
[0003] The Downs Process uses a molten salt electrolyte consisting
of a mixture of NaCl, CaCl.sub.2 and BaCl.sub.2 in order to reduce
the melting temperature of the electrolyte to slightly below
600.degree. C. This makes the process more practical compared to
using pure NaCl which has a much higher melting point of about
800.degree. C. Nevertheless, operating an electrolytic process at
such temperature is difficult and presents numerous operating
constraints. Because of the high operating temperature of the Downs
Process, the cell design uses concentrically cylindrical cathodes,
wire mesh diaphragms, and anodes rather than the much more space
efficient stacked multiple flat electrode and diaphragm element
configuration that is normally used in electrochemical engineering
practice. Furthermore, the high operating temperature would make a
flat wire-mesh steel diaphragm so soft that it would be
mechanically unstable and flap back and forth between anode and
cathode causing partial shorting/arcing and thereby causing holes
to be burned in the diaphragm. Holes in the diaphragm would allow
back mixing of sodium produced at the cathode and chlorine produced
at the anode, thereby causing low current efficiency of the cell.
On the other hand, the concentric cylindrical configuration of the
steel diaphragm between the electrodes avoids this difficulty
because a wire-mesh cylinder is mechanically much stiffer and
mechanically more stable than a flat wire-mesh screen of the same
kind.
[0004] The above-described concentric cylindrical cell design of
the Downs Process, necessitated by the high operating temperature
of about 600.degree. C., also means that the Downs cell has very
poor space efficiency. This translates directly into high capital
and operating cost per unit production.
[0005] The high operating temperature of the Downs cell in
combination with the fact that the molten mixed salt electrolyte
has a freezing temperature only about 20.degree. C. below the cell
operating temperature makes smooth operation of the cells
difficult. Cell `freeze-ups` and other "upsets" are frequent and
result in unusually high operating labor requirements for an
industrial electrolytic process. This in turn is also the reason
why the Downs Process is not amenable to automation. Lithium is
currently produced by a modification of the Downs process.
[0006] In recent years fundamental physico-chemical studies have
been carried out on battery applications using electrolytes based
on non-aqueous solvents for alkali metal chlorides that do not
crystallize at ambient temperature. See J. Electrochem. Soc. Vol.
143 No. 11, pages 3548-3554, November 1996; and U.S. Pat. No.
5,855,809, disclosures of which are incorporated by reference.
[0007] There is an increasing need to develop an electrolytic
process that can be used to produce an alkali metal more
economically. There is also a need to develop a process that can
improve operability such as, for example, making automation
possible.
SUMMARY OF THE INVENTION
[0008] An electrolysis process that can be used for producing an
alkali metal from an alkali metal halide is provided, which
comprises electrolyzing an electrolyte composition comprising, or
produced by combining, at least one alkali metal halide and a
co-electrolyte in which the co-electrolyte comprises or is produced
by combining (a) at least one halide of Group IIIA, Group IB, or
Group VIII and (b) a halide-donating compound.
BRIEF DESCRIPTION OF DRAWING
[0009] FIG. 1 is a laboratory H cell used for electrolysis in the
Examples section of the application.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The electrolysis is carried out at a low temperature. The
term "low temperature" refers to a temperature lower than about
200.degree. C. It can be in the range of from about 20.degree. C.
to 200.degree. C., preferably about 50.degree. C. to 150.degree.
C., and most preferably about 100.degree. C. to 150.degree. C. The
electrolysis is preferably carried out under a condition that
produces a molten layer of alkali metal at the cathode and hydrogen
at the anode.
[0011] The invention electrolysis process can also comprise or
consist essentially of electrolyzing an electrolyte composition
comprising or consisting essentially of at least one alkali metal
halide and a co-electrolyte consisting essentially of (a) at least
one halide of Group IIIA, Group IB, or Group VIII and (b) a
halide-donating compound.
[0012] Any alkali metal halide can be used in the invention. The
term "alkali metal" refers to lithium, sodium, potassium, rubidium,
cesium, francium, or combinations of two or more thereof. The
preferred alkali metals are sodium and lithium. Most preferred is
sodium. Alkali metal produced in the electrolysis process disclosed
herein is preferably in bulk quantity that can be transported in
substantially pure form. The presently preferred alkali metal
halide is sodium chloride, widely available and used to produce
sodium by electrolysis.
[0013] The halide for the co-electrolyte is a halide or halides of
Group IB, Group IIIA, or Group VIII elements, or combinations of
two or more thereof, hereinafter referred to as "co-electrolyte
halide(s)", The term "Group IB", "Group IIIA", or "Group VIII" used
in the invention refers to the CAS version of the Periodic Table of
the Elements, CRC Handbook of Chemistry & Physics, 67th
edition, 1986-1987, CRC Press, Boca Raton, Fla. Examples of
suitable Group IB halides include copper halide such as copper
chloride and copper bromide; silver halide such as silver chloride;
and gold halide such gold chloride. Examples of Group IIIA halides
include aluminum halide such as aluminum chloride and aluminum
bromide; boron halide such as boron chloride; gallium halide such
as gallium chloride; indium halide such as indium chloride;
thallium halide such as thallium chloride. Examples of Group VIII
halides include one or more of iron halides such iron chlorides and
iron bromides; cobalt halides such as cobalt chloride and cobalt
bromide; and nickel halide such as nickel chloride and nickel
bromide; rhodium halide such as rhodium chloride; and rhenium
halide such as rhodium chloride. The preferred halide for the
co-electrolyte is a strong Lewis acid such as aluminum trichloride
or boron trichloride. Most preferred is aluminum trichloride.
[0014] The molar ratio of the alkali metal halide to the
co-electrolyte halide(s) can be from about 1:1 to about 1.1:1. The
alkali metal halide is preferably present in only a slight excess
for ease of operability. The alkali metal halide and the
co-electrolyte metal halide(s) can form a reaction product under
the electrolysis conditions.
[0015] The halide-donating compound for the co-electrolyte is
preferably a molecule capable of reacting with a Lewis acid,
preferably a strong Lewis acid, by donating a halogen atom.
Preferably the halide-donating compound is RSO.sub.2X,
RP(O)X.sub.2, or combinations thereof where R is --CX'.sub.3,
--N.dbd.PX.sub.3, --(CX.sub.2).sub.nCX.sub.3, or combinationls of
two or more thereof, X is a halogen atom, X' is hydrogen, a
halogen, or combinations thereof, and n=3-7. Most preferably X is a
chlorine atom. More preferably, the halide-donating compound is a
largely or substantially inorganic compound. Especially preferred
halide-donating compounds include, but are not limited to, methane
sulfonyl chloride, trichlorophosphazophosphoryl chloride
(Cl.sub.3P.dbd.NP(O)Cl.sub.2), trichlorophosphosphazosulfonyl
chloride (Cl.sub.3P.dbd.NSO.sub.2Cl), and combinations of two or
more thereof. These halide-donating compounds can be produced by
any means known to one skilled in the art such as, for example, the
means disclosed in J. Electrochem. Soc. Vol. 143 No. 11, pages
3548-3554, November 1996.
[0016] The halide-donating compound can be present in an
approximately 1:1 ratio with the co-electrolyte halide(s), i.e.,
the halide-acceptor(s), excluding the amount of co-electrolyte
halide(s) previously stated to be necessary in combination with the
alkali metal halide. That is, the co-electrolyte halide(s) serves
two functions, and the amounts required are additive. This 1:1
ratio combination can be present in any quantity as long as the
reaction product of the alkali metal halide and co-electrolyte
halide(s) is soluble in it at the low temperatures discussed above.
This can vary with each such combination. For example, sodium
tetrachloroaluminate, the reaction product of sodium chloride and
aluminum trichloride, has a significant solubility in the above
co-electrolytes and is different for each co-electrolyte. If a
second co-electrolyte (Group IB, IIIA or Group VIII, for example)
halide is present, the molar ratio of the total of the first and
second co-electrolyte halides to the alkali metal halide can also
be 1:1. For example, an electrolyte comprising methanesulfonyl
chloride-aluminum trichloride-sodium chloride can have a
corresponding molar ratio of 1:1.4:0.4, respectively. Of this
mixture, 1.0 mol of aluminum trichloride is required for the
methanesulfonyl chloride and 0.4 is required for the sodium
chloride, making the total amount 1.4 moles.
[0017] The electrolyte composition can be produced by any means
known to one skilled in the art. For example, an alkali metal can
be combined with a co-electrolyte halide or a halide-donating
compound followed by combining the resultant combination with a
halide-donating compound or a co-electrolyte halide. Such combining
can be mixing or reacting under any suitable condition. Wishing not
to be bound by theory, an intermediate can be formed by contacting
an alkali metal halide and co-electrolyte. The intermediate can
then be electrolyzed to produce a desired alkali metal. For
example, sodium tetrachloroaluminate, the reaction product of
sodium chloride and aluminum trichloride, can be used for producing
sodium under electrolysis condition.
[0018] The anode of an electrolysis cell can consist of
electrically conductive carbon, nickel, an DSA.RTM. (dimensionally
stable anode), a Group VIII metal oxide, or a Group VIII metal such
as platinum, which is not corroded by the anodically liberated
halogen such as, for example, chlorine gas. On the cathode side of
the cell the cathode itself can consist of electrically conductive
carbon, stainless steel, iron, nickel or other Group VIII metal.
The diaphragm separating the anode and cathode is a porous,
non-reactive material such as glass-fiber fabric, fritted glass, a
porous ceramic material, asbestos or a non-reactive polymeric
screen or fabric.
[0019] An alkali metal halide and any of the co-electrolytes can be
individually introduced into an electrolysis cell in any order.
They can also be introduced contemporaneously. For example, an
alkali metal halide can be combined with any co-electrolyte (either
co-electrolyte halide or halide-containing compound) before being
introduced to an electrolysis cell.
[0020] According to the invention, moisture is preferably excluded
because water can react with, and hydrolyze, a halide of an
inorganic acid in the electrolyte. This can be achieved by
constructing the cell in a gas-tight, hermetically sealed fashion.
In order to achieve a high degree of space efficiency it is
advantageous to construct the cell in the well-known
stacked-multiple-flat-plate arrangement. Known electrochemical
engineering practices are used in providing means for circulating
and replenishing the electrolyte, for providing electrolysis
current, for handling cathode product liquid alkali metal and anode
product chlorine gas. The cell is generally operated in a
continuous mode. Because of its low temperature operation the
invention process is well suited for automated operation. The
overall design of the electrolytic cell can be based on the
cylindrical cell design used for the Downs process, and can even be
a modified Downs cell. Alternatively the design can be based on a
horizontal bank of stacked vertical anode and cathode plates, such
as those used for the production of caustic soda from aqueous
sodium chloride. The cathode can be provided with a physical means
for transporting cathodically produced mixture of liquid alkali
metal and electrolyte to an external, heated collection chamber.
During operation of the cell, the liquid alkali-electrolyte mixture
produced can share in the cathode function with the cathode.
Physical means for transporting liquid alkali metal away from the
cathode can be machined channels or grooves, a system of holes, or
use of porous materials having interconnected pores permitting
molten alkali metal to flow into the collection vessel. There are
numerous other ways of performing this function which one skilled
in the art can devise depending on one's preference.
[0021] The liquid sodium metal from the electrolytic cell can be
purified by heating the impure sodium to above 100.degree. C.,
whereupon the sodium, which has a melting point of 97.5.degree. C.,
forms a melt which floats on the surface of the remaining
co-electrolyte. Sodium can then be separated from the
co-electrolyte by decantation, filtration or other means. If
desired, the sodium can be further purified by fractional
crystallization or by solvent extraction, i.e., heating in a
solvent, removing the bulk of the solvent by decantation,
filtration or other means, and removing traces of solvent from the
sodium by heating under vacuum. The above solvent should have some
solubility for the co-electrolyte and essentially no solubility for
the sodium. Preferably the solvent has a boiling point above
100.degree. C. under process conditions. Preferred solvents are
dioxane or other high-boiling polyethers.
[0022] Sodium can also be purified via formation of a dispersion
with an inert hydrocarbon with a boiling point above the melting
point of sodium, such as mineral spirits or mineral oil. These
hydrocarbons are insoluble with the ionic liquid and have a lower
density. Sodium can be purified by forming a dispersed sodium
solution at a temperature above100.degree. C., followed by cooling
and settling. High speed agitation (>2000 rpm) can be used to
form the sodium dispersion. A dispersing agent such as one or more
fatty acid can also optionally be added in this step. On stopping
the agitation, the occluded ionic liquid forms a bottom layer
containing any sodium chloride or other salts. The upper layer
contains sodium in a dispersed form, useful for promoting many slow
organic reactions.
[0023] A preferred process comprises (1) providing an electrolytic
cell and an electrolyte composition comprising the alkali metal
halide and a co-electrolyte containing the combination of (a) a
halide or halides of Group IIIA, Group IB, or Group VIII elements
and (b) a halide-donating compound; (2) carrying out the
electrolysis in the electrolytic cell in the presence of the above
electrolyte composition at a temperature below about 200.degree.
C., thereby producing the alkali metal, generally a layer of molten
metal, at the cathode and halogen at the anode; (3) if the
temperature used for step 2 is below the melting point of the
alkali metal, especially in a continuous process, raising the
process temperature, i.e., the electrolysis cell and electrolyte,
to above the aforesaid melting point; (4) removing the layer of
molten alkali metal from the electrolytic cell; (5) separating the
alkali metal from any electrolyte impurity by any means known to
one skilled in the art such as fractional crystallization or
solvent extraction and solvent removal during which some
electrolyte is recovered as recovered electrolyte; and optionally
(6) recycling the recovered electrolyte. The scope and quantity of
alkali metal halidem at least one halide, and halide-donating
compound, electrolysis cell, process condition, etc. are the same
as that disclosed above.
[0024] The above process can be carried out in a batch or
continuous mode. The electrolysis process is preferably carried out
at a temperature above the melting point of the alkali metal, if
steps 1 to 4 are carried out continuously where additional alkali
halide is added to the electrolysis cell as the alkali metal is
continuously removed from the cell. For example, if the alkali
metal is sodium, the above electrolysis is preferably carried out
at a temperature below about 150.degree. C., but above the melting
point of sodium. Also preferably the invention is carried out in an
electrolysis cell containing a porous diaphragm.
EXAMPLES
Example 1
Preparation of Room Temperature Ionic Liquids
[0025] 1A. Synthesis of trichlorophosphazosulfonyl
chloride-aluminum trichloride-sodium chloride
[0026] Trichlorophosphazosulfonyl chloride was synthesized
according to the procedures disclosed in J. Electrochem. Soc., Vol
143, No, 11, p. 3548 (1996). A room temperature (about 25.degree.
C.) ionic solution was prepared by initially adding
trichlorophosphazosulfonyl chloride (188.7 g, 0.75 mole) to a 500
ml round-bottomed flask equipped with an overhead stirrer,
thermocouple, and inert nitrogen blanket heated with a heating
mantle. The solid was initially melted by heating to 40.degree. C.
under nitrogen. Aluminum trichloride (149.8 g, 1.125 mole) was
slowly added as a solid over a one hour period, keeping the
temperature at 40-45.degree. C. The solution was then heated to
80.degree. C. and sodium chloride (21.9 g, 0.375 mole) was added
over a fifteen minute period. The solution was held for one hour at
80.degree. C. and then cooled to room temperature. The solution was
a clear brown solution with no sediment.
[0027] 1B. Synthesis of methanesulfonyl chloride-aluminum
trichloride-sodium chloride
[0028] A room temperature ionic solution was prepared by initially
adding methanesulfonyl chloride (458.4 g, 4.0 mole) to a flask same
as described above. Aluminum trichloride (746.8 g, 5.6 mole) was
added over a three hour period, keeping the temperature below
50.degree. C. The solution was then heated to 60.degree. C. and
sodium chloride (93.6 g, 1.6 mole) was added over 0.5 hour, keeping
the temperature below 70.degree. C. The reaction was cooled to room
temperature to give a clear green solution.
[0029] 1C. Synthesis of
trichlorophosphazophosphorylchloride(Cl.sub.3P.dbd-
.NPOCl.sub.2)aluminum trichloride-sodium chloride
[0030] Trichlorophosphazophosphorylchloride was synthesized
according to the literature (see J. Electrochem. Soc., Vol. 143,
No.11, p 3548 (1996)). A room temperature ionic liquid was prepared
by the addition of trichlorophosphazophosphorylchloride (46.1 g,
0.17 mole) into a 250 ml round-bottomed flask in a dry box. The
flask equipped as above was then warmed to 35.degree. C. to melt
under a nitrogen purge so the solution could be stirred. Aluminum
trichloride (27.4 g, 0.20 mole) was added slowly under nitrogen
over a 40 minute time period, keeping the temperature between
40-50.degree. C. The solution was then heated to 100.degree. C. and
sodium chloride (2.0 g, 0.034 mole) was added over a 15 minute
period. The solution was cooled to room temperature to give a
clear, dark brown solution.
Example 2
[0031] An electrochemical H cell, as shown in FIG. 1, was used. The
cell has an extra-coarse sintered glass frit (reference numeral 3)
separating the anode (14) compartment and cathode (14) compartment,
inlet (12 and 22) and outlet (11 and 21) for an argon purge for
each of the anode and cathode compartments, and an Agilent.RTM.
E3617A DC Power Supply (reference numeral 1) with 0-60V DC and 1.0
amp capacity. Reference numeral 2 is a solid brace while 13 and 24
respectively show anolyte (15) level and catholyte (25) level. The
argon outlet for both the anode and cathode lead to an aqueous 33%
potassium iodide scrubber in-line with a Tedlar.RTM. balloon gas
sample collector. The anode was a vertical 10.times.12.times.2 mm
nickel strip and the cathode a vertical 10.times.12.times.2 mm 316
stainless steel strip. The nickel anode was approximately 5 mm from
the extra-coarse frit, the 316ss cathode was approximately 10 mm
wide, and the frit was 5 mm wide, so the electrodes were a total of
20 mm apart.
[0032] The potassium iodide scrubbers were used to trap chlorine
co-product from the anode and to check the effluent from the
cathode compartment for any chlorine that might have migrated
across the sintered glass frit separator. Tedlaro balloon from the
anode outlet was used to trap any volatile organic methyl chloride
and other volatile organic byproducts from chlorine reaction with
the methanesulfonyl chloride. Chlorine was analyzed by iodometric
titration and the methyl chlorides by gas chromatography.
Tedlar.RTM. balloon from the cathode was used to analyze hydrogen
and any co-mixing of anode solutions.
[0033] An electrolyte (48.0 g) was used, which consists of
methanesulfonyl chloride-aluminum trichloride-sodium chloride in a
1:1.4:0.4 molar ratio, respectively, together with 2 g excess
sodium chloride in the cathode compartment. The argon flows were
set at 1.6 ml/min for the anode and the cathode compartments. The
electrolytes were heated to 50.degree. C. in an oil bath. The
voltage was increased to 30V. The voltage was held constant for 1.8
hours to give a current in the range of 0.07-0.14 amps for an
integrated average of 0.10 amps (a theoretical chlorine production
of 3.32 mmol). During the running time bubbles were observed at the
anode and black dendrils were formed on the face of the
cathode.
[0034] At the end of the run the power was turned off and both
anode and cathode compartments were purged with argon at 50.degree.
C. into the scrubber solutions to remove any dissolved chlorine and
other soluble volatiles. Two argon sparges of 45 and 30 minutes
each were made to free the solution of dissolved gases. A total of
2.48 mmol chlorine (74.7% efficiency) was recovered from the anode
caustic scrubber by iodometric titration and 0.02 mmol of chlorine
(0.8% of total) incorporated into a mixture of methyl chloride,
methylene chloride, chloroform, and carbon tetrachloride from the
Tedlar.RTM. balloon. The cathode showed no chlorine from the
caustic scrubber and 0.04 mmol of hydrogen from the GC analysis of
the Tedlar.RTM. balloon.
[0035] The dendrils on the cathode were confirmed by x-ray
diffraction and electron microscopy to be a mixture of metallic
sodium with traces of ionic bath components. No elemental aluminum
was detected by x-ray diffraction, showing that aluminum ion was
not reduced to aluminum metal.
Example 3
[0036] The same electrochemical H-cell and analyses used in Example
2 were used here. An electrolyte (71.6 g) was used consisting of
trichlorophosphazosulfonyl chloride-aluminum trichloride-sodium
chloride in a 1:1.5:0.5 molar ratio together, respectively, with 2
g excess sodium chloride in the cathode compartment. The argon
flows were set at 4.4 ml/min for the anode and cathode
compartments. The electrolyte was heated to 103.degree. C. in an
oil bath and the voltage was increased to 29.9V. The voltage was
held constant for three hours to give a current in the range of
0.13-0.21 for an integrated average of 0.19 amps (a theoretical
chlorine production of 10.9 mmol). A total of 6.6 mmol chlorine
(60.6% efficiency) was recovered. The sodium together with bath
impurities was scraped in an inert atmosphere dry box from the
cathode and confirmed by x-ray diffraction and volumetric hydrogen
measurement on treatment with anhydrous methanol (10.2 mmol, 46.7%
efficiency in sodium).
[0037] The cell was run for an additional 10 hours at 103.degree.
C. at 29.9V. The current remained in the 0.12-0.20 amp range for an
additional 10 hours with no noticeable sign of bath decomposition.
The chlorine efficiency averaged 81% over this time. The sodium was
scraped from the cathode at 3-4 hour intervals. It was analyzed by
hydrogen volume measurement on addition of methanol. The sodium
efficiency averaged 55% by this technique. The sodium was also
confirmed by x-ray diffraction. As before, the dendrils on the
cathode were confirmed by x-ray diffraction and electron microscopy
to be a mixture of metallic sodium with traces of the ionic bath
components, with no elemental aluminum.
Example 4
[0038] The same electrolyte and electrochemical H-cell used in
Example 3 was used here. The cell conditions were also the same
except the electrolyte was heated to 150.degree. C. at the same
29.9 V. The voltage was held constant for 4.25 hours to give a
current in the 0.17-0.21 amp range for 4.25 hours with no sign of
bath decomposition. The measured chlorine efficiency averaged about
105% during this time (the estimated experimental error in analysis
is about +5% to -5%). Most of the sodium was floating on the top of
the electrolyte solution, and was filtered. A small amount of
sodium was attached to the cathode and was removed by scraping. The
total recovered sodium was 85% of the theoretical amount of sodium,
as determined by hydrogen volume analysis.
Example 5
[0039] The same electrolyte and H-cell was used as Example 3. The
electrolyte was heated to 105.degree. C. and the voltage was
increased to 29.9V for 5.0 hours to give a current in the 0.11-0.13
amp range (a theoretical chlorine production of 12.1 mmol). A total
of 6.3 mmol of chlorine was recovered (51.9% efficiency). Sodium
was filtered and the electrodes were scraped of sodium.
[0040] The same bath was recycled for the identical run to give a
49.6% chlorine efficiency. These runs demonstrate the robustness of
the baths for recycle.
Example 6
[0041] An electrolyte (66.8 g) was used consisting of
trichlorophosphazophosphorylchloride
(Cl.sub.3P.dbd.NPOCI.sub.2)-aluminum trichloride-sodium chloride in
a 1:1.17:0.17 molar ratio together, respectively, with 2 g excess
sodium chloride in the cathode compartment. The argon flows were
set at 4.4 ml/min as in Example 3. The electrolyte was heated to
103.degree. C. in an oil bath and the voltage was increased to 50V.
The voltage was held constant for 3.5 hours to give current in the
range 0.045-0.10 amps(theoretical chlorine production of 5.0 mmol).
A total of 2.48 mmol Cl.sub.2 was determined by iodometric
titration (49% efficiency). As before, the dendrils on the cathode
were confirmed by x-ray diffraction and electron microscopy to be a
mixture of metallic sodium with traces of the ionic bath
components, with no elemental aluminum.
[0042] The above experiments demonstrate the preparation of sodium
metal electrochemically at low temperatures in the presence of an
ionic salt solution. The largely or substantially inorganic salt
electrolyte is liquid with low viscosity at room temperature and
unreactive with co-product chlorine and sodium metal under the
reaction conditions. Under the same conditions these largely or
substantially inorganic electrolytes show significantly higher
current densities than organic electrolytes and allow a lower
electrolysis temperature and process ease of operation because of
their lower melting points. They also show little or no reactivity
with nascent chlorine co-product.
[0043] A low temperature process can offer many potential
advantages such as, for example:
[0044] More space and labor efficient stacked multiple flat
electrode assembly usually used in electrochemical practice rather
than the concentrically cylindrical cathode and anode configuration
required at the high temperature (>600.degree. C. ) of the Downs
Process,
[0045] Energy and operability advantages of the lower
temperatures,
[0046] Reduction of chlorine release and exposure potential,
and
[0047] Dramatic reduction in cost of manufacturing
[0048] These largely or substantially inorganic electrolytes have
the advantages of lower melting points leading to lower
electrolysis temperatures, higher current densities under
comparable conditions (6 fold increase), and are generally less
expensive and more commercially viable.
* * * * *